1. Technical Area
For sealing off shaft bushings, sealing arrangements are used which are designed to retain the lubricants in the interior of the housing and which prevent dust, dirt, and the like from entering the housing interior from outside. Quite varying designs are used for seals. In this context, great significance attaches, inter alia, to the size of the installation space. The smaller the installation space, the more difficult it is to seal it off. In every case, the goal is a long service life for the seal and the least possible wear and tear. The latter is also achieved by using appropriate materials such as PTFE compounds.
2. Background Information
From German Laid-Open Print 33 16 063, a sealing ring is known which is provided with a sealing sleeve made of PTFE. The sealing sleeve is formed in a trumpet-like shape opposite the space to be sealed off, and, on the side facing the shaft to be sealed off, it has recirculation elements that act in a hydrodynamic manner.
The present invention is based on the objective of refining the known sealing ring by achieving a seal that is more reliable even in extreme operating conditions while retaining the simplest possible mode of manufacture. The sealing arrangement is designed so as to have minimal weight, a long service life, and minimal wear and tear. Any deviations from circularity, a center offset of shaft and bore hole, lack of roundness in the shaft, and the like are designed to be compensated for. And this is so even at high peripheral speeds, high temperatures, and any lubrication deficits that might arise at the sealing location.
The above-mentioned objective is achieved by the features of claim 1. Subclaims 2 through 12 contain advantageous embodiments of the idea of the invention.
Based on the related art, the sealing arrangement is provided with a sealing sleeve made of polymer material, having a retaining segment and a sealing segment. The retaining segment is connected to a supporting body, and the sealing segment surrounds a shaft to be sealed off, under radial biasing on the peripheral side. The sealing segment is provided on its side facing the shaft with a surface profiling for recirculating the lubricating oil. The configuration according to the present invention provides that the connecting diameter (interior diameter of the enclosing part) is 1.0 to 1.05 times the shaft diameter, plus four times the thickness of the sleeve. The configuration of the sealing sleeve is therefore designed on the basis of the shaft diameter. The latter is determined in relation to the connecting diameter of the enclosing part and the subsequent design steps for configuring the sealing ring are carried out. Designated as the enclosing part is the part of the sealing arrangement on which the sealing sleeve is secured.
The thickness of the sleeve is selected so that it is {fraction (1/20)}-{fraction (1/300)}, preferably {fraction (1/50)}-{fraction (1/200)}, of the shaft diameter. In this manner, the sleeve obtains a particularly planar shape. In addition, the length of the sealing segment of the sleeve is selected so as to be especially long, so that it is 3 to 15 times, preferably 4 to 12 times, the thickness of the sleeve. In this way, the contact pressure of the sealing segment on the shaft is reduced, and the loss due to friction is less. In addition, less material is used due to the especially thin configuration of the sleeve.
In addition, it is advantageous if the sleeve, in the sealing segment is smooth on its rear side and is configured so as to be grooved in a spiral manner on its sealing side. These grooves allow an efficient recirculation of the lubricant. These grooves in a generally familiar manner can be configured, in cross-section, out of symmetrical triangles or out of asymmetrical saw teeth. In this context, the more planar surfaces of the saw teeth are configured in the direction of the space to be sealed off. The depth of the grooves is selected so as to be especially high and is 70-90% of the thickness of the sleeve. Approximately 85% has proven to be preferable. The grooves themselves are extended up to the retaining segment of the sealing sleeve. As a result, good recirculation of the lubricant is assured. To prevent lubricant from escaping to the outside when the shaft is standing still, the edge of the sealing sleeve facing the ambient environment can be configured as a sealing bulge. A point-shaped interruption on one of the forward grooves is also possible here.
The interior diameter of the sleeve is executed so that the sealing segment contacts the shaft on at least four grooves. The most advantageous number is 4 to 12 grooves, but the preferred range is 7 to 8 grooves. In certain application cases, it can be advantageous to introduce multi-thread grooves.
Finally, it should be emphasized that the material used for the sealing sleeve is preferably a PTFE compound (polytetrafluoroethylene) or a fluorothermoplast.